The conventional technique used to produce this type of piece consists in hot stamping a precut sheet blank, using a tool comprised of a die and a one-piece punch, which molds the blank against the walls of the die in a single pass.
The production of flanged edges with this type of tool poses problems.
Actually, during the downward motion of the punch into the die, the compaction of the blank acts on the sides of the punch between it and the die, producing friction, which entails problems in the bending zone of the blank and likewise in the flanged edges of the finished piece.
It is thus in the bending zone of the blank, where folding to 90 degrees generally occurs, that a phenomenon called squeezing-out occurs, which consists in stretching of the fibers with a reduction in the thickness of the wall of the blank, a tendency of the fibers to settle in the direction of the center of the die and expulsion of the impregnation resin toward the exterior.
This phenomenon is relatively weak if the length of the flanged edge is also relatively small, for example less than 30 mm. On the other hand, the friction is very strong. Moreover, the thinner the wall of the flanged edge, the more this squeezing-out phenomenon is significant.
At the location of the flanged edges, the poor conversion of the vertical forces of the punch into horizontal forces pressing the flanged edges can result in fiber confusion, sliding of the layers of the blank, local variations of thickness and deformation or twisting of the fibers of said flanged edges, as well as of the folding zones of the piece that has been formed in this way.
Finally, with this sort of tool, removal from the jig can entail some problems, due to the compaction of the flanged edges, and it is completely impossible to obtain edges with a tilt towards the interior.
The purpose of this invention is to eliminate the aforementioned difficulties.